1. FIELD OF THE INVENTION
The invention relates to a microwave integrated circuit device and more particularly to a microwave integrated circuit device which is small in size, and inexpensive, but highly reliable and in which a solid circuit such as a waveguide and a microwave integrated circuit (hereinafter abbreviated to MIC) such as a strip line are integrally constructed.
2. DESCRIPTION OF THE PRIOR ART
According to a conventional method of connecting a waveguide with a MIC such as, for example, a strip line, the MIC is provided with a coaxial connector and the coaxial connector is coupled through a separate coaxial waveguide adapter to the waveguide. According to another similar conventional method, an antenna pattern is formed on the front surface of the MIC substrate, that part of the conductor lying on the rear surface of the MIC substrate which corresponds to the antenna pattern is removed, and the MIC substrate is placed in the waveguide so that the strip line on the MIC substrate may be directly coupled electromagnetically to the waveguide.
However, these conventional methods have drawbacks: the provision of the MIC in the waveguide causes a transmission loss to degrade the electric characteristic of the MIC device, it is not easy to attach or detach the MIC to or from the waveguide, and the MIC device is expensive. To eliminate these drawbacks, a MIC device has been proposed in which a MIC is mounted on the inner surface of the short-circuiting plate of a waveguide so as to directly couple the MIC electromagnetically to the waveguide, and the MIC can be easily attached to or detached from the waveguide with a good airtight seal, and which can be fabricated inexpensively. With this MIC device proposed, however, the detector diode or the mixer diode is situated so close to the short-circuiting member of the waveguide that the electromagnetic coupling of the diode to the electromagnetic field in the waveguide tends to be loose coupled. This leads to the drawback that the reception sensitivity of the diode cannot be made sufficiently high, In order to eliminate the above drawback, a MIC device has also been proposed in which the conductor disposed on the rear surface of the substrate which are opposite to the MIC patterns to be connected with the anode and the cathode of the detector or mixer diode, are removed in part and in which a groove for enhancing the electromagnetic coupling between the diode and the electromagnetic wave in the waveguide is formed in the short-circuiting member of the waveguide. This MIC device is diclosed in the U.S. Patent Application Ser. No. 954,118, filed as a prior application before this one by the same inventor (who has made this invention). With this MIC device, the electromagnetic wave in the waveguide leaks into the coupling groove to increase the electromagnetic coupling to the detector diode. On the other hand, however, the provision of the coupling groove makes the frequency characteristic sharp so that the frequency band in which high reception sensitivities are attained, is narrowed. In extreme cases, the resultant frequency band may fail to contain the design frequency and it is not always possible to obtain a sufficient reception sensitivity at the desired frequency.